msm: cleanup: union gsi_wdi2_channel_scratch2_reg

Remove __packed from the usage of union gsi_wdi2_channel_scratch2_reg
__packed is only needed in the union definition.

include/linux/msm_gsi.h:
union __packed gsi_wdi2_channel_scratch2_reg {
    ...
}

Bug: 140528058
Test: build pass
Change-Id: Ie3a6ebbe26af09d845f4a3f3f756b381a8e47a21
Signed-off-by: neoyu <neoyu@google.com>